Dude....... Xebec, the times when he clashed with Harald and caused a 5km wide shockwave which knocked everyone up, literally killed an admiral. Sure, we don't exactly know how the fight went like but this event was meant to hype Xebec's power.
So by your own words, you believe DR made Xebec so significantly powerful he was able to solo skysplit, yet two admiral level characters managed to combine their attack and kill him?